Artificial bristle



July 9, 1940. H. A. NEVILLE VET AL ARTIFICIAL BRISTLE Filed April 2, 1940 INVEN M fl, mm

Patented July 9, 1940 UNITED sr TEs PATENT OFFICE ARTIFICIAL BRISTLE Application April 2, 1940, Serial No. 327,419

16 Claims.

Our invention relates to artificial bristles and more particularly to bristles having a filamentary core and a tapered coating that give the bristles the general tapered form andfiexibillty characteristic of natural bristles. Because of their taper and flexibility characteristics, as well as resistance to solvents and other liquids these artificial bristles may be used advantageously instead of natural bristles, such as paint brushes,

in and when mounted therein will not objectionably bowor curl.

This application is a continuation-in-part of our application Serial No. 243,318, filed December 1, 1938 (abandoned in favor of this application on 1.) April 6, 1940), and the claims herein cover the artificial bristles. The method and apparatus for making these bristles is claimed in our copending application Serial No. 294,572, filed September 13,

In accordance with our present invention we have found that tapered artificial bristles having superior properties may be produced by immersing a filament in a relatively viscous coating solution and withdrawing the filament from the solution at a changing rate of withdrawal, increasing or decreasing. The filament, as withdrawn, has a coating of variable thickness of the coating material. The more rapid the rate of withdrawal of the filament the greater the amount of viscous solution retained on the filament and accordingly the thicker the layer of adhering coating. Decreasing the rate of withdrawal produces the opposite effect, namely, a decrease in the thickness of the coating. Because 5 of these phenomena we are able to produce upon a filament a coating of uniformly decreasing thickness, which is in efiect a taper, by gradually increasing the rate of withdrawal of the filament from the coating solution in which it isimmersed. The form of the coated filament is like that of an animal (e. g., hog), bristle, in that it has a butt end of relatively large diameter and a tip end of relatively small diameter, with proportion-.

' ately varying diameters in between the butt and tip ends.

To product the desired type of taper on the coated filament as above described, we havq found that it is desirable to have present certain conditions, as follows:

The coating solution, which is to be applied to the filament for increasing its resistance to water, solvents, alkalis, acids, etc., and which in some instances may also be used for tapering the filament, must be substantially prevented from flowing along the filament core after the coated filament is withdrawn from the solution. Otherwise, the material would build up in places and be too thin in other places causing non-uniformity of coating thickness as well as non-uniformity of taper. The same is true where a separate solution is used for tapering. We have found that any substantial amount of flowing may be prevented by one or a combination of the following methods:

A. Using a very volatile solvent, e. g., acetone, in the coating material solution so that as soon as the coated filament is withdrawn from this solution the solvent will evaporate rapidly and cause gelationv or other solidification of the coating material about the core filament. This rapid solidification of the coating upon exposure to the atmosphere will cause it to retain its desired position on the filament. The rate of evaporation may be accelerated by partial evacuation of the space surrounding the coated filament or by providing a current of air to carry away the vapors.

B. Rapidly decreasing the temperature of the fluid coating material on the filament immediately after it leaves the reservoir of coating solution, so that the material gels or solidifies before it has an opportunity to flow on the filament. Suitable refrigerating means such as a current of cold air or an artificially refrigerated enclosure for the coated filament might be used to hasten the solidifying or gelling of the coating.

C. Rapid solidification of the fluid coating material on the filament may also be obtained by using the coating material in the form of a thixotropic dispersion that will set to a gel very quickly upon application to the filament.

Unless one or moreof these several methods of producing rapid gelation or their equivalent is utilized, the fluid coating will tend to flow along the filament or will be drawn into droplets or beads on the filament by the forces of surface tension. Slow evaporation of the solvent or slow cooling, either of which will produce a gradual increase in viscosity, are not sumcient to avoid entirely the fiow of the coating or its collection into droplets.

If the entire filament to be coated is wound upon a frame and is immersed in the coating solution and withdrawn, whether it be of a length adequate for making one bristle or several, the withdrawal of the frame and filament from the solution would be at a predetermined rate of acceleration or deceleration to effect the desired taper. Such an operation would be used where it is desired to produce in batches one or several bristles at a time, and then repeating the operation for each subsequent batch of bristles. However, if it is desired to produce the bristles continuously, especially on a large production scale, a continuous length of filament stock would be used and would be withdrawn continuously but the rate of withdrawal would be intermittently accelerated or decelerated. By this procedure a continuously coated filament having thick and thin sections at regular intervals Will be produced. The rate of taper and the length of the tapered portions of the filament may be controlled by the withdrawal cycle such that the continuously coated filament having alternately thick and thin portions may be cut at points of maximum and minimum thickness to produce individual bristles, the length and degree of taper of each such bristle being determined, as mentioned above, by the nature of the withdrawal cycle.

The filamentary core materials that may be used in our invention vary Widely in their characteristics and may be selected from one or more of the following classes of materials: textile fibers, such as natural silk; or certain artificial silks, such as rayon, and the polyamides disclosed in Carothers Patent No. 2,130,948, issued September 20, 1938, or certain vinyl polymers extruded into fibers, cotton, regenerated cellulose, cellulose acetate, other cellulose esters and ethers, glass; metals such as steel, copper, copper alloys, aluminum, aluminum alloys and silver, the non-ferrous metals being preferred because of their resistance to rust; and any other similar suitable materials that can be spun or drawn into continuous filaments which have the fiexibility and strength required for brush bristles. The choice of these materials depends somewhat upon the use to which the final bristle is to be put and is dictated by such factors as tensile strength, resistance to solvents, flexibility and stifiness of the materials.

The core filaments may be individual filaments or may consist of a strand or thread made up of a number of filaments. We have found that threads composed of a plurality of continuous filaments substantially parallel or with a slight twist are desirable and ofier advantages over threads made of spun fibers. Different sizes of yarns may be used so that a better filling of the voids is obtained on blending the resulting bristles. As an example, a coarse product is obtained by winding frames with one strand (composed of many individual filaments), of 150 denier cellulose acetate yarn. An intermediate product is obtained from frames wound with one strand of denier cellulose acetate yarn and a fine product from frames wound with one strand of 45 denier cellulose acetate yarn. These yarns may be wound in multiple. For example, if three strands of 45 denier are wound as a unit, a product comparable to that from one strand of denier yarn is obtained. However, there is some improvement in stiffness, due to the trefoil structure.

Where the filament, used for the bristle core, is not subject to attack by solvents or liquids with which it will come into contact in use, such as for example a metal filament, only a single coating (tapered) will be required for the filament. However, when filaments subject to attack by liquids are used, such as for example silk filaments, the filament will first be coated with a protective coating material which is ree. g., a cellulose acetate coating, this tapered coating is in turn covered with a protective outer coating. The two protective coatings may be of 'uniform thickness-not taperedsince the tapered coating will provide the desired taper similar to that of natural bristles.

As above suggested, the artificial bristles may be made up acording to a number of difierent combinations depending upon the types of materials used, particularly the relative resistance of the materials to attack by solvents. Examples are:

A. A solvent resistant filament core with a single solvent resistant tapered coating;

B. A non-resistant filament core with a protective coating thereon and a tapered coating on top of the protective coating;

C. A non-resistant filament core, a protective coating on the core, a non-resistant tapered coating and a protective coating over the tapered coating.

A presently advantageous commercial form of our artificial bristle comprises a non-resistant (cellulose acetate) core, a protective coating (resinous varnish) and a resistant tapered coating (cellulose triacetate).

The coating materials used for coating or tapering the filament cores may be selected from a large class of different substances and are normally used in the form of solutions or dispersions. These materials include both thermosetting and thermoplastic substances and may be plastic, resinous or non-resinous. An important characteristic of the tapering solution is that it will set or gel rather quickly when de- 1 Plastics Cellulose esters and ethers Cellulose acetate Cellulose triacetate Cellulose aceto-butyrate Resinous varnishes Cleo-resinous varnishes Alkyd resin varnishes Oil modified alkyd resin varnishe Urea-formaldehyde resin varnishes (straight or plasticized) Phenol-formaldehyde resin varnish Oil modified phenol-formaldehyde varnishes Cashew nut shell oil varnish Polyamz'des Hexamethylene adipamide Tetramethylene sebacamide The solvents to be used in the coating solutions may vary widely in their characteristics, and their selection will depend somewhat upon theproce'dure adopted for gelling or solidifying the coating material on the filament promptly upon withdrawal of the filament from the coating mixture. Where the gelation or solidification is dependent solely or primarily upon the volatility of the solvent such rapid vaporizing solvents as acetone, methyl acetate, ethyl acetate, methyl formate and benzene and the like, and

certain of the chlorinated solvents such as chicroform and dichlorethylene may be used. Where I one of the other means above described is used for accelerating the gelation or solidification-of the coating on the filament slower drying solvents such as for example certain of the refined petroleum and coal tar distillates, e. g., xylene, varsol and high-flash naphtha may be used.

In accordance with our invention the artificial bristles may be made by applying one or several coatings to the filament core material. For example, where the filament core material consists of metal, only one type of coating will be required for giving the bristle the desired resistance to water, acid, alkalies, etc., and also for effect-- ing the desired taper of the bristle. In such a case the coating material may advantageously be selected from the above mentioned classes of resins or varnishes which would give the filament the desired resistance to attack by liquids and the necessary tensile strength where required. This varnish or resin coating may be applied in one application, that is, one immersion of the core material in the coating solution and withdrawal therefrom, or several of such treatments.

In the case of certainother filament core materials, particularly some of the textile fibers which are not resistant to the common lacquer solvents such as acetone and the like, we have found it advantageous to apply several different types of coatings to the filament core. Some of these coatings serve principally the purpose of giving the filament the desired resistance and strength and the other coatings the desired taper required to simulate natural bristles.

The artificial bristles of our invention and method of production may be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing in which Fig. 1 is a diagrammatic representation of the filament core material wound upon a frame preliminarily to dipping in the coating material;

Fig. 2 is an elevational perspective view, partly in section, of the coating and tapering system illustrating the coated filament being withdrawn from the coating container;

Fig. 3 is a longitudinal sectional view of a piece of filament coated by the system shown in Fig. 2;

Fig. 4 is a diagrammatic representation of a system for continuous coating and tapering of the filament; and

Fig. 5 is a longitudinal sectional view 'of a portion of a tapered coated bristle having a metal core and one layer of coating.

Referring now to the several figures in the drawing, generally in the order in which they occur, there is shown in Fig. 1 a frame II) with the filament ll wound thereon, the filament in this specific but non-limiting embodiment of the invention being a cellulose acetate fiber. The filament is wound on the frame ill by clamping the frame in a mechanical winder (not shown) with a traveling guide so that as the frame is rotated the guide moves from one end of the frame to the other and thereby produces a spiral wind of the filament on the frame. An example of the pitch of this winding is ten turns to the inch. The ends of the filament may be fastened to the frame in any suitable manner such as by tying to a cross member of the frame.

The textile fiber filament, i. e.', cellulose acetate in this example, being wound on the frame, the next step is to dip the wound frame in a bath containing a suitable varnish or resin solution to, coat the textile filaments. A system suitable for that purpose is shown in Fig. 2. As shown in that figure a dipping tank 13 is approximately filled, for example, within one-half of an inch of the top of the tank, with a resin solution/indicated at Id. In this specific arrangement the dipping tank is of suflicient capacity to accommodate only one\ frame, (a laboratory size being 13 inches long, 7 inches high, and V inch wide), but it is to be understood that in commercial production larger tanks would be used, such as to accommodate two or more rows of frames. In such an arrangement the filaments may be dipped and coated and after coating may be cut at the top and bottom to form the individual bristles;

and the plurality of frames may be held in parallel and dipped together in one operation. To facilitate handling of the filaments after coating the uppermost portion of the filaments, e. g., inch, is not immersed in the coating material and this uncoated portion is cut off when the filament is cut into individual bristles.

The means for withdrawing th frame and coated filament from the dippingt nk l3 comprise two cords l5 having hooks l6 for engaging the eye extensions l2 on the frame ill. The cords l5 extend and are movable over pulleys l1 rotatably mounted on an axle [8. The cords 15 also extend over a second pair of pulleys l9 rotatably mounted on an axle 20. The cords are joined at the ends remote from the dipping tank, to a member 2| by means of the hook and eye arrangement shown generally at 22. The member 2|, which is in the form of a fiat, narrow board or metal strip is attached to or is integral with a plunger 23 which is adapted to work in an oil cylinder 24. The cylindrical container 25,

which is attached to the top of the plunger 23, y

and the inlet pipe 26 with valve 21 are not used in this preliminary coating process but are used in the tapering treatment described below.

The coating solution M in the clipping tank l3 may be selected as above noted from a large number of resin solutions. We have produced very satisfactory results with a China-wood oil modified phenol formaldehyde enamel which is made up according to the following formulae under Example I: 1

Another example of a coating composition that height and connecting the cords we have found to give satisfactory results is as follows:

55 Castor oil modified alkyd resin (50% solids and 50% oil modified) 35 Xylol 10 In the specific case being described, we use for the coating material, the enamel composition shown above under Example I. The frame Ill with filament ll wound thereon is immersed in the coating solution M for a short time, r example 1-2 minutes.

The withdrawal of the filament and frame from the coating composition l4 shown in Fig. 2 is carried out by raising the plunger 23 to its full l5 with the frame ID by means of the hooks IS. The plunger 23 is then permitted to travel downward in the oil cylinder 24. In this example the time of withdrawal was about 1 minute and 15 seconds, and the frame is withdrawn at a constant or steady rate of withdrawal as the plunger slowly drops through the oil. To facilitate drying of the coating on the filament during the withdrawal operation, additional means such as electric fans 28, as shown in Fig. 2, may be used These fans will blow a current of air against the coated filament as it emerges from the coating tank and it is desirable to have these fans blow the air upward at an angle of about along thefront and back edge of the top of the tank I3. These two streams of air meet at the frame and follow it upward during the withdrawal.

The coated filament still wound on the frame and after air drying to permit the major portion of the solvent to evaporate, is baked in an oven at about 150 C. for a period of about 45 minutes to 1 hour. The resinous enamel coating thus produced on the filament serves as a protection of the textile fibers of this filament, e. g., cellulose acetate, from the solvent action of the tapering solution which is next to beapplied as follows.

The coated filament still wound on the frame is allowed to cool after the above baking treatment and is then again dipped in the tank l3, from which the resin solution has been removed and a suitable tapering solution substituted. In this case the tapering solution consisted of cellulose acetate with acetone solvent and a plasticizer. When using cellulose acetate we have found that the low viscosity type cellulose acetate is desirable and a satisfactory example is the type LL-l made by the Hercules Powder Company. The purpose of using low viscosity cellulose acetate is to provide as high solid content as possible for a given viscosity; the range of solid content used was from about 15% to 30%. Another specific example of a suitable cellulose tapering solution is cellulose aceto-butyrate in acetone solution.

We have found that it is important to have good control of the viscosity of the tapering solution, and we have determined the permissible viscosities by testing such solutions in a tube having two marks eight inches apart. The test is made by noting the time required for a steel ball (in this case having a diameter of inch) to fall between the two marks in the cellulose acetate solution and we have obtained satisfactory results with solutions tested in this manner having variations in viscosity from about 6 seconds to 15 seconds at 25 C. on-this arbitrary scale. We prefer a range of approximately 8 to 12 seconds; a 10 second solution being a good average. It the viscosity is too great or the speed of withdrawals of the filament too fast as above explained, the solution fills in or forms a web between adjacent threads. Also if the viscosity is too low there is a tendency to produce a wavy coating which has in effect a modi fied droplet formation.

In carrying out the tapering process we have found it important to have the tapering solution, e. g., cellulose acetate, come as near the top of the container [3 as possible. In this connection we have obtained satisfactory results by filling the container to about A inch from the top with the tapering solution. If the solution is not near enough to the top the coating material starts to fiow down along the filament when the latter is withdrawn and a poor taper results. This is apparently caused by the atmosphere just above the solution in the container being saturated with the solvent vapor, which prevents rapid evaporation of the solvent contained in the coating material on the filament core.

The frame with coated filament wound thereon as described above, is immersed in the tapering solution now contained in the tank l3 for a period of about 1 to 2 minutes and then withdrawn from this tapering solution at a steadily increasing rate. This withdrawal is accomplished by the same procedure described above for the first coating except that a stream of mercury or other suitable liquid is fed through the pipe 26, controlled by valve 21, into cylindrical container 25. Instead of a liquid a suitable solid, which will pour, such as for example sand, may be supplied to the container 25. The'accumulating increase-in weighton the plunger 23 produced by this increasing amount of mercury in the container 25 causes the speed of descent of the plunger 23 to steadily increase against the opposing forces due to the viscosity of the solution, and thereby increase the speed of withdrawal of the frame from the tapering solution. This speed may be so adjus d as to effect the withdrawal of the frame fronTthe tapering solution in a period of about 39" to 35 seconds depending upon the size of the frame. By steadily increasing the rate of withdrawal, no droplets of excess material are formed on the filament and the desired taper is produced by the varying amount of cellulose acetate material retained over the length of the filament. The current of air from the electric fans 28 or other suitable means may also be used in this instance to facilitate drying of the tapering solution if desired.

After the frames, with tapered coating on the filament, are air dried to remove the major portion of the acetone solvent, requiring about 1 hour at room temperature, the frames are given another dipping in the resin solution, the same or similar to that used for producing the first coating described above. It will be understood for this operation that the tapering solution is removed from the container l3 and substituted by a resin solution such as described above under Example I for effecting the final protective coat on the tapered filament. To avoid filling and refilling of the tank l3 with the above solutions separate dipping tanks may be employed for the coating and tapering compositions.

After the tapered and coated filament is wi-th-, drawn from the final coating solution it is again baked for a period of about 2 hours at about 120 C. This bakingtreatment will vary of course with different types of coating and tapering s lutions. The above example of temperature and time is based upon use of the black phenol formaldehyde enamel described under Example I, and the use of cellulose acetate plasticized with the plasticizer known as Santicizer M-17 for the tapering solution. If the cellulose acetate is not plasticized and a urea formaldehyde resin is used, the baking time would be about 45 minutes at about 150 C.

When the final baking operation above described has been completed the individual strands are cut from the frames at top and bottom, the cutting at the top being from about of an inch to f r; of an inch above the limit of the "cellulose acetate coating, that is the tapering solution. For making one type of brush bristle the bundle of tapered filaments is cut to a length of about 5 inches and is now ready to be blended with others of the same and different sizes to make up the paint brush formula.

Measurements of the tip and butt ends of the coated and tapered filaments described above The coated and tapered section of filament shown in Fig. 3 is an example of the type of filament produced by the above described process. In this showing the diameter of the bristle has been greatly enlarged and is out of proportion with respect to the length shown, for the sake of clarity of illustration. As shown, this filament consists of the filament core material 29, the inner resinous protective coating 30 covered by the tapered coating 3| and finally an outer protective resinous coating 32. When using very small diameter filament cores the applicants have found it advantageous to start the tapered coating a short distance back from the end of the filament core which forms the tip end of the bristle, as indicated at the left end of the bristle in Fig. 3. As shown there the very tip end of the filament core 29 is covered with the protective coatings 30 and 32 but is not covered with the An alternative procedure to that described above, in which the filament is given three coats of material, is to apply directly to the textile filament core, such as for example natural silk, the cellulose acetate tapering solution using a solvent that will not damage the textile filament; and then cover the cellulose acetate tapered coating with an outer protective coating of resinous or other coating material. This procedure eliminates the use of the inner protective coating.

In Fig. 4 there is illustrated diagrammatically a system that might be used for carrying out in a continuous manner the coating and tapering operations described above. This system comprises a reel 34 having wound thereon the filament core material 35 which during operation is unwound from this reel and first run over a guide roller 36 and into a coating bath 31. The coating material shown at 38 in this bath may be any of the coating or tapering solutions described above. The filament is guided through this bath by means of the guide roller 39 and the coated filament 40 upon leaving the bath is pulled upward into a solvent vaporization chamber 4|. This drying chamber causes volatilization of the major portion of the solvent from the coated filament. After this treatment the coated filament next passes through a baking chamber 42 wherein the coating is heat treated to produce the desired hardness.

The filament is drawn through the system above describedby means of friction rollers 43, which are driven by any suitable means (not shown). When the filament is being given a resinous or other type'of protectivev coating at a constant rate of withdrawal from the coating solution the rollers 43 will be so actuated as to cause the filament to be drawn through the system at a constant rate. However, when the filament is being tapered the mechanism is so arranged as to withdraw the filament from the tapering solution at an intermittently accelerated and decelerated rate of withdrawal. This may be effected through the intermediary of elliptic gear or similar wellknown conventional means which per se, are not a part of this invention. The coated or tapered filament 44 upon leaving the withdrawal mechanism 43 is guided between the cutting blades 45 for cutting the filament into any desired lengths.

In Fig. 5 there is shown an example of a bristle containing only one layer of coating and tapering material. This bristle consists of a metal filament core 46 and a tapered resinous coating 41. This type of bristle may be produced by the same process described above but omitting the application of an inner and outer coating of uniform thickness. In this case the resinous or other suitable resistant coating material is used as the tapering material, that is, the metal filament core is withdrawn only one time and at a varying rate of withdrawal from the coating material so that the material will be deposited upon the filament core in tapered form. This type of coating and tapering with one material may also be applied to other core materials than metal, examples of which are given hereinabove.

The term thermosetting" used herein in connection with certain of the resinous coatings indicates a resin material that is chemically hardened into a permanent infusible form by ouring, that is, heating the material until it hardens into this form. The term thermoplastic indicates a resinous material that hardens upon cooling but may be softened again by heating.

' The term hardened as used in the claims applies generically to both types of resinous materials or other coatings hardened in place on the filament core.

For purposes of general identification the artlficial bristle of this invention is defined in the claims as one having an external shape and size approximating that of a natural bristle. It is to be understood that this refers only to the general order of size and shape and is not restrictive to the exact dimensions or proportions of natural bristles. Also the taper of the coating of the artificial bristle may vary appreciably from the taper of natural bristles.

The word filament as used in the specification and claims herein is used in a generic sense and is intended to include the various forms of fibers, filaments, strands, threads, etc., made up of one or more of suitable core materials such as those described above.

Various modifications and changes may be made in the processes, materials and equipment described hereinabove without departing from the scope of our invention, some of the novel features of which are defined in the appended ,claims. We claim:

1. An artificial bristle comprising a filament core and a tapered coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

2. An artificial bristle comprising a textile filament core and a tapered coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

3. An artificial bristle comprising a metal filament core and a tapered coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

4. An artificial bristle comprising a silk'filament core and a tapered coating of such thickness and taper that the external shape andsize of the bristle approximates that of a natural bristle.

5. An artificial bristle comprising a filament core and a tapered plastic coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

6. An artificial bristle comprising a filament core and a resinous tapered coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

7. An artificial bristle comprising a 'filament core and a thermoplastic tapered coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

8. An artificial bristle comprising a filament core and a vinyl resin tapered coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

9. An artificial bristle comprising a filament core and a vinyl acetal tapered coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle 10. An artificial bristle comprising a filament core and a vinyl formal tapered coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

11. An artificial bristle comprising a filament core and a polyamide tapered coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

12. An artificial bristle comprising a filament core and a cellulose ester tapered coating of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

13. An artificial bristle comprising a filament core, a tapered coating on said core and a protective coating covering said tapered coating said coating being of such thickness and taper that the external shape and size of the bristle approximates that of a natural bristle.

14. An artificial bristle comprising a filament core normally subject to attack by organic solvents, a protective solvent resistant coating covering said core and a solvent resistant tapered coating covering said protective coating.

15. An artificial bristle comprising a filament core, a protective coating on said core, a tapered coating covering said protective coating and a protective coating covering said tapered coating said coatings being of such thickness and said tapered coating having such a taper that the exshape and size of the bristle approximates that' of a natural bristle.

HARVEY A. NEVILLE. WILLIAM C. FORBES. 

